I had entered a land of nakedness. The first and entirely unexpected sign was the backside of an old woman emerging from a raspberry bush as I cycled past. The shock caused me to swerve convulsively, but she carried on picking the fruit, unconcerned. Soon, on the river bank, I was encountering row upon row of nude, white bodies lapping up the late afternoon sun. Further on, families were enthusiastically barbecuing, picnicking and playing beach volleyball in the nude.

We were cycling on the Donauinsel, a long, artificially created strip of land between two arms of the Danube, where the river bypasses Vienna. It is the unorthodox (and unpublicised) route heading out of the city on to the Donau Radweg (the Danube cycle path that hugs the great river from Passau in Germany to Vienna and beyond).

The Donauinsel, I belatedly discover, is a Viennese bastion of Freikörperkultur or "free body culture". In practice, this means public nudity. This land of the naked goes on for some 5km, and then we were back to everyday life where people walk around in clothes.

Not that touring the Donau Radweg, one of Europe's most popular cycling paths, is ever mundane. Every kilometre has a tale to tell.

See over there on the south bank of the river? The green slopes of Heiligenstadt, Beethoven's summer retreat from the imperial city of Vienna and inspiration for his Pastoral Symphony. Pedal a little further, that's the wooded hill of Kahlenberg rearing almost 1,000ft over the river. From Kahlenberg's summit, on September 12 1683, King Jan Sobieski of Poland led his cavalry in a glorious charge on the Ottoman army that besieged the Hapsburg capital, causing the Turks to flee in frenzied disorder and the Grand Vizier of the Ottoman empire to conclude, "Allah, in His wisdom, has not yet permitted us to capture Vienna."

As dusk approached, we cycled into the quaint, tranquil town of Korneuburg and swiftly located a good-value hotel from the Oekotel chain. (Hotels, guesthouses and zimmer beckon at every bend along the river - there's no need to pre-book.)

Next morning, we joined the ranks of perspiring, Lycra-clad heavyweights, parents towing kids, post-middle-aged couples and parrots (cyclists decked out in the latest plumage) on the Donau Radweg proper - our destination Linz - 228km upstream.

We cycled along the wooded, riverside track, lulled by the lapping of the water. Meadows of wild flowers splashed the rolling countryside. Window-boxes brimmed with bright red geraniums. Soon we stopped at a cyclist's jausenstation (purpose-built snack bar) and swiftly downed brimming half litres of Puntigamer beer flavoured with lemon. Grilled Danube trout looked tempting and then how could we resist the local speciality, marillen knödel (apricot dumplings) with hot cream?

We had found our rhythm - one hour or so of cycling, followed by a spritzer at one of the frequent jausenstations, as we crossed and re-crossed the Danube.

Late afternoon, seeking a change from the cycling crowds, we diverted from the river-hugging path on to a lonely, country lane meandering towards Krems. At the village of Grafenwörth we found the local wine festival was in uproarious progress. We had not intended to stop, but the wine producers manning the stalls beckoned us to sample their wares, and a 12-piece brass band was belting out sentimental Austrian lieder. There were firemen in uniform, hunters in green lederhosen and felt hats, women in frilly blouses; and everyone had quarter-litre glasses of the local white wine, grüner veltliner, in their hands. Very soon quarter-litre glasses were in our hands too.

We ordered more wine which was accompanied by black bread smeared with fried pig fat (a local delicacy). We were sharing a table with a fit, keen-looking cyclist and his girlfriend. "Started the day in Korneuburg," we mentioned with a touch of pride. "Ja. It is one of my training routes - takes just over an hour," the parrot remarked. It had taken us eight. We changed the subject. Later his girlfriend informed us that he was the local cycling champion.

A handsome, scarred hunter bowed low and requested a dance with my female cycling companion. I offered my arm to a red-faced grandmother who whisked me energetically around to the oompah of the band provoking much guffawing from the wine-growers.

It was almost dark as we fled unsteadily across mercifully flat land to the comforts of the Hotel Steigenberger Avance in Krems, gateway to the Wachau proper.

Next day, we climbed to the heights above the valley. A fully grown stag stared at us before bounding magnificently away. Hearts pounding, we climbed the brow of the hill and were rewarded with a view of the Danube winding through wooded gorges. Then it was 10km of exhilarating, steep downhill, through terraced vineyards sparkling in the morning sun. Rejoining the river at a little shingle beach, I peeled off shorts and T-shirt and stepped into the cold, fast-flowing stream.

Just a little further down the river, we passed the ruined hilltop castle at Dürnstein where Richard the Lionheart was incarcerated in 1192. According to legend, the minstrel Blondel, wandering the Danube castles in search of his master, strummed a verse on his lute at the dungeon walls, and received an answering verse sung from within. The tiny village, with its numerous wine taverns, posh hotels and restaurants and river cruise ships, has grown rich on this fortuitous connection with the English monarch.

But now we were approaching the most magnificent baroque structure of the whole Danube: the Benedictine monastery of Melk, a glorious, orange-yellow, cream and gold-gilded church-palace commanding the clifftop.

Next day we set out along dramatic gorges plunging steeply to the river. Approaching the town of Grein, dominated by its musty-yellow, Hapsburg castle, we crossed the swift-flowing river on a tiny, wooden ferry designed exclusively for cyclists.

Two hours later and we were labouring towards Mauthausen, another supremely attractive medieval river village but also the site of a concentration camp. From 1938 until the Allied liberation, 110,000 prisoners perished, most of exhaustion, starvation and disease from working the nearby granite quarries.

It was early evening before we entered the long, verdant park and recreation zone which heralds the approach of Linz, Austria's third-largest city and next year's European Capital of Culture. The city was gearing up for the annual festival of local composer Bruckner which starts mid-September and runs until early October. Situated a few metres from the cycle path is the state-of-the-art, four-star Spitz Hotel, opened only last year - an architectural celebration of the cultural renaissance of the city. Soon we were resting aching legs, celebrating with an excellent glass of local apricot brandy.

That evening we strolled down by the crowded, grassy banks of the river as a half-moon peeked out from behind the foothills of the Alps, the evening lights glittered across the water and from the huge riverfront stage, Bruckner's eighth symphony resounded to the skies.